I kind of understand... its like one of those spanish jokes that don't make sense in English...

Well, maybe....

Think of the English saying "Even Homer sometimes nods." If I were to translate this into Japanese, I'd have to explain who Homer is, and what the concept implies. Fortunately, the Japanese have their own equivalent: 弘法にも筆の誤り （こうぼうにもふでのあやまり）. Kobo-Daishi was a Buddhist priest who is sort of the patron saint of calligraphy, and the saying implies that even Kobo slipped in his calligraphy from time to time and made a mistake. Thus the equivalent to "Even Homer sometimes nods."

Many kotowaza have English proverb parallels:
猫に小判 = Pearls before swine
言わぬが花 = Silence is golden
紺屋の白袴 = The cobbler's sons have no shoes
蛙の子は蛙 = Like father, like son.

Some have entered into English usage:
出る釘は打たれる = The nail that sticks up will be hammered down

But most are just... well, they need explanation.
残り物には福がある "There is luck in the ones left till last"
大同小異 "Differences are overshadowed by similarities"
油を売る "To sell oil (meaning = to waste time talking)."